A posh London conference tackles the Polio vaccine controversy.

Medical conferences are fairly predictable affairs: a lot of hypotheses, an onslaught of data and, for the most part, congeniality-at least outwardly. But last week's gathering on the origin of AIDS at London's posh Royal Society-complete with afternoon tea-took on the excited and at times contentious tenor of a courtroom trial. On one side, Edward Hooper, author of "The River: A Journey to the Source of HIV and AIDS," who believes that the virus was most likely introduced into humans through an experimental polio vaccine given in Africa in the late 1950s. On the other, scientists Hilary Koprowski and Stanley Plotkin who created the vaccine at Philadelphia's Wistar Institute. Hooper's presence as a non-scientist amidst hundreds of medical experts was remarkable, but the gravest implication of the theory is impossible to ignore: scientific culpability for a plague that has killed 18 million worldwide. "He deserves," says one of the conference organizers, "a hearing."

Scientists generally agree that HIV jumped to humans from chimpanzees, which harbor a close relative of the virus-most likely when African hunters were bitten or scratched by the animals. But Hooper argues instead the virus made its leap because chimp kidney cells were used in polio vaccine preparation nearly half a century ago. In addition to methodically detailing how it might have happened in his 1,070-page book published last year, Hooper presented two new "smoking guns" at the London conference: recollections by an anonymous source who said chimp kidneys were extracted at Wistar's African research camp and by a vet who says he was told they were sent to the United States and other vaccine-making sites. "I would propose," said Hooper, "that there is now a case to answer."

For Koprowski, Plotkin and many other scientists, that answer came in the form of long-awaited test results of vaccine remnants, which had been stored for more than 40 years in Wistar's freezer. Three independent labs found absolutely no trace of chimp virus, HIV or chimp cells. The findings were bolstered by testimony, presented by Plotkin, from 16 sources involved in vaccine preparation who said chimps were never used, and by recent research dating the emergence of HIV back to the 1930s-long before the vaccine's introduction. The polio theory has been "mortally wounded," said one participant at the close of the meeting. "Once and for all," says Plotkin, "this idea should be laid to rest."

But given the intensity of the debate and ongoing disputes over the evidence, that's unlikely to happen. Public health officials, meanwhile, worry that the most dangerous ramification could be public mistrust of vaccines. The current oral polio vaccine (unrelated to Wistar's) is on track to eradicate the disease worldwide by 2005. Renewed threat of an old plague is a horror nobody on either side can bear.